Alkali-free glass and preparation thereof

ABSTRACT

The present invention provides the composition of an alkali-free glass composition containing no alkali metal oxide and the preparation thereof. The alkali-free glass comprising substantially no alkali metal oxide according to the present invention comprises 60 to 70 wt % of SiO 2 ; 1 to 3.5 wt % of B 2 O 3 ; 1 to 13 wt % of Al 2 O 3 ; 8.5 to 14 wt % of MgO; 1 to 3 wt % of CaO; 4 to 7 wt % of SrO; and 0.5 to 7 wt % of BaO, based on the total weight of oxides present therein.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a Continuation Bypass of International ApplicationNo. PCT/KR2012/007015 filed on Aug. 31, 2012, and claims the benefit ofKorean Patent Application Nos. 10-2011-0089047 and 10-2012-0096356 filedon Sep. 2, 2011 and Aug. 31, 2012, all of which are hereby incorporatedby reference in their entirety for all purposes as if fully set forthherein.

TECHNICAL FIELD

The present invention relates to a glass manufacturing technology, andmore particularly to an alkali-free glass composition comprising noalkali metal oxide and the preparation thereof.

BACKGROUND ART

Glasses, flat glasses in particular, are variously applied to windowpanes, window screens for vehicles, and mirrors and come in manydifferent forms depending on its type and use.

Among various types of flat glasses, alkali-free glass substrates arewidely used in flat panel display devices such as a liquid crystaldisplay (LCD), a plasma display panel (PDP) and an organicelectroluminescent (EL). This is because an alkali glass substratecontaining an alkali metal oxide may deteriorate film characteristicsdue to the diffusion of alkali metal ions contained in the glasssubstrate into a film.

However, glass used in flat panel display substrates requires variouscharacteristics.

For example, a glass for flat panel display substrates should be lightweight. In particular, as display devices such as televisions andmonitors are becoming larger and larger recently, glass substrates usedtherein are also enlarging in size. The enlarged size of the glasssubstrate may increase the bending of the glass substrate due to theweight thereof. Accordingly, in order to prevent such a problem, thereis a need to manufacture a light weight glass substrate. Also, such alight weight glass substrate may be used in small portable devicesincluding a mobile phone, a PDP and a notebook to increase portability.

In addition, a glass for flat panel display substrates should haveproper melting properties (fusibility). If the melting property of theglass decreases, much time and energy is required for the glass to melt,and bubbles or foreign substances may generate in the glass to cause afault. The bubbles or foreign substances present in the glass may hinderthe penetration of light, deteriorating the quality of the glass,thereby making it difficult to use the glass for display devices.

Further, a glass for flat panel display substrates should haveheat-resistance. For example, flat panel display devices such as aTFT-LCD may be subject to heat-treatment during the preparation thereof,at which a glass substrate may be exposed in rapid heating and coolingconditions. If the glass has insufficient heat-resistance, the glass maydeform or bend, and may also even break due to tensile stress resultingfrom heat. In addition, in the case of a glass for a TFT-LCD, if itsheat-resistance is low, a thermal expansion difference between the glassand the materials of TFT occurs and the pixel pitch of the TFT maydistort to cause a display fault.

DISCLOSURE Technical Problem

Accordingly, the present invention is designed to solve theabove-mentioned problems, and therefore it is an object of the presentinvention to provide a light weight alkali-free glass having goodmelting property and easy processability, and a method for preparing thesame.

Other objects and advantages of the present disclosure will beunderstood from the following descriptions, and become more apparentfrom the Examples. Also, the objects and advantages of the presentdisclosure can be easily acknowledged to be implemented by meansrepresented in the claims and a combination thereof.

Technical Solution

In order to accomplish the above object, in accordance with one aspectof the present invention, there is provided an alkali-free glasscomprising substantially no alkali metal oxide and comprising 60 to 70wt % of SiO₂; 1 to 3.5 wt % of B₂O₃; 1 to 13 wt % of Al₂O₃; 8.5 to 14 wt% of MgO; 1 to 3 wt % of CaO; 4 to 7 wt % of SrO; and 0.5 to 7 wt % ofBaO, based on the total weight of oxides present therein.

Preferably, the alkali-free glass has a density less than 2.55 g/cm³, acoefficient of thermal expansion of 3.0×10⁻⁶/K to 4.0×10⁻⁶/K, atemperature less than 1620° C. at a viscosity of 10² dPas, and atemperature less than 1260° C. at a viscosity of 10⁴ dPas.

In accordance with another aspect of the present invention, there isprovided a display device comprising the above-mentioned glass.

Preferably, the display device is a liquid crystal display.

Further, in accordance with still another aspect of the presentinvention, there is provided a method for preparing an alkali-freeglass, comprising combining raw materials of glass to obtain analkali-free glass comprising substantially no alkali metal oxide andcomprising 60 to 70 wt % of SiO₂; 1 to 3.5 wt % of B₂O₃; 1 to 13 wt % ofAl₂O₃; 8.5 to 14 wt % of MgO; 1 to 3 wt % of CaO; 4 to 7 wt % of SrO;and 0.5 to 7 wt % of BaO, based on the total weight of oxides presenttherein.

Preferably, the combination of raw materials is carried out for BaO tobe substantially contained in the alkali-free glass.

Also, it is preferred that the alkali-free glass prepared by theabove-mentioned method has a density less than 2.55 g/cm³, a coefficientof thermal expansion of 3.0×10⁻⁶/K to 4.0×10⁻⁶/K, a temperature lessthan 1620° C. at a viscosity of 10² dPas, and a temperature less than1260° C. at a viscosity of 10⁴ dPas.

Advantageous Effects

In accordance with the present invention, an alkali-free glasscomprising substantially no alkali metal oxide can be provided.

Particularly, in accordance with an embodiment of the present invention,an alkali-free glass having a low density can be provided. Accordingly,even if the size of the substrate is big, the alkali-free glass having alow density can be less subject to bending due to its heavy weight,thereby being suitably used in large display devices, for example atelevision and a monitor. In addition, the glass of the presentinvention can be adjusted to be light weight, and thus can be used as aglass substrate in small portable devices including a mobile phone, aPDP and a notebook to increase portability.

Also, the alkali-free glass according to an embodiment of the presentinvention exhibits a low T₂ where T₂ is a temperature at a viscosity of10² dPas, from which the melting property of the glass is improved, andexhibits a low T₄ where T₄ is a temperature at a viscosity of 10⁴ dPas,from which the processing temperature of the glass decreases and theglass can be easily processed. Thus, as the melting temperature andprocessing temperature of the glass decreases, energy and time requiredfor melting and processing the glass can be reduced.

In addition, the alkali-free glass according to an embodiment of thepresent invention can exhibit a low coefficient of thermal expansion toprevent the glass from thermal contraction, deformation, bending orbreaking even if the glass is exposed in various heat-treatmentconditions during preparing flat panel display devices such as aTFT-LCD. Also, the coefficient of thermal expansion of the glass issimilar to that of the materials of TFT, thereby effectively preventinga display fault which occurs due to the distortion of a pixel pitch.

Therefore, the alkali-free glass according to the present invention ispreferably used as a substrate for flat panel display devices such as aliquid crystal display (LCD), a plasma display panel (PDP) and anorganic electroluminescent (EL).

DESCRIPTION OF DRAWINGS

The accompanying drawings illustrate preferred embodiments of thepresent disclosure and, together with the foregoing disclosure, serve toprovide further understanding of the technical spirit of the presentdisclosure. However, the present disclosure is not to be construed asbeing limited to the drawings.

FIG. 1 is a flow chart schematically showing the procedure of a methodfor preparing an alkali-free glass in accordance with an embodiment ofthe present invention.

BEST MODE

Hereinafter, preferred embodiments of the present invention will bedescribed in detail with reference to the accompanying drawings. Priorto the description, it should be understood that the terms used in thespecification and the appended claims should not be construed as limitedto general and dictionary meanings, but interpreted based on themeanings and concepts corresponding to technical aspects of the presentinvention on the basis of the principle that the inventor is allowed todefine terms appropriately for the best explanation.

Therefore, the description proposed herein is just a preferable examplefor the purpose of illustrations only, not intended to limit the scopeof the disclosure, so it should be understood that other equivalents andmodifications could be made thereto without departing from the spiritand scope of the disclosure.

The glass of the present invention is an alkali-free glass in which analkali metal oxide is not substantially contained. That is, thealkali-free glass of the present invention comprises no alkali metaloxide or only a trace amount of alkali metal oxide therein. The term “atrace amount” which is used herein refers to an extremely small amountwhich is negligible as a component of the glass as compared to othercomponents. For example, if an alkali metal oxide such as Li₂O, Na₂O andK₂O is present in an amount of 0.2 wt % or less as a component of theglass, it is considered that the alkali metal oxide is not substantiallycontained in the glass.

The alkali-free glass of the present invention comprises SiO₂, B₂O₃,Al₂O₃, MgO, CaO, SrO and BaO as the components thereof.

Preferably, the alkali-free glass of the present invention comprisesSiO₂ in an amount of 60 to 70 wt % based on the total weight of oxidespresent therein. SiO₂ is an oxide which produces a glass-forming networkstructure, and contributes to increase the chemical resistance of theglass and provide a proper coefficient of thermal expansion to theglass. However, when the amount of SiO₂ is extremely high, thecoefficient of thermal expansion may decrease and the devitrificationproperty of the glass may be poor. When the amount of SiO₂ is extremelysmall, it may cause the reduction of chemical resistance, the increaseof a density and coefficient of thermal expansion, and the reduction ofa deformation point in the glass. Accordingly, the glass of the presentinvention comprises SiO₂ in an amount of 60 to 70 wt %, preferably 62 to68 wt %, more preferably 64 to 66 wt %.

Also, the alkali-free glass of the present invention comprises B₂O₃ inan amount of 1 to 3.5 wt % based on the total weight of oxides presenttherein. B₂O₃ is an oxide which produces the network structure of aglass, and contributes to enhance the characteristics of the glass, forexample, the increase of melting reactivity, the decrease of acoefficient of thermal expansion, the improvement of devitrificationproperty and chemical resistance, such as resistance to buffered HF(BHF), and the decrease of a density. However, when the amount of B₂O₃is extremely high, it may cause the reduction of acid resistance, theincrease of a density, and the reduction of a deformation point in theglass, thereby deteriorating the heat-resistance of the glass. When theamount of B₂O₃ is extremely small, the effect obtained from theinclusion of B₂O₃ becomes insufficient. Accordingly, the glass of thepresent invention comprises B₂O₃ in an amount of 1 to 3.5 wt %,preferably 2 to 2.9 wt %.

In addition, the alkali-free glass of the present invention comprisesAl₂O₃ in an amount of 1 to 13 wt % based on the total weight of oxidespresent therein. Al₂O₃ contributes to enhance the high-temperatureviscosity, chemical stability and resistance to thermal shock of theglass and increase the deformation point and Young's modulus of theglass. However, when the amount of Al₂O₃ is extremely high, it may causethe deterioration of devitrification property and the reduction ofresistance to hydrochloric acid and BHF, and the increase of aviscosity. When the amount of Al₂O₃ is extremely small, the effectobtained from the inclusion of Al₂O₃ becomes insufficient and theelastic modulus of the glass may be reduced. Accordingly, the glass ofthe present invention comprises Al₂O₃ in an amount of 1 to 13 wt %,preferably 9 to 13 wt %, more preferably 11 to 13 wt %.

In the alkali-free glass of the present invention, the sum of eachamount of SiO₂ and Al₂O₃ (the amount of SiO₂+Al₂O₃) is preferably in therange of 73 to 82 wt %. Within such a concentration range, the effectobtained from the inclusion of SiO₂ and Al₂O₃ may be more improved, andthus the reduction of the coefficient of thermal expansion and thedeterioration of the devitrification property may be prevented. Morepreferably, in the alkali-free glass of the present invention, theamount of SiO₂+Al₂O₃ is in the range of 76 to 79 wt %.

Also, the alkali-free glass of the present invention comprises MgO in anamount of 8.5 to 14 wt % based on the total weight of oxides presenttherein. MgO is an alkali earth metal oxide and contributes to inhibitthe increase of a coefficient of thermal expansion and the reduction ofa deformation point and enhance melting property in the glass. Inparticular, MgO may reduce the density of the glass, therebycontributing to the lightening of the glass. However, when the amount ofMgO is extremely high, it may cause the deterioration of devitrificationproperty and the reduction of resistance to an acid and BHF in theglass. When the amount of MgO is extremely small, the effect obtainedfrom the inclusion of MgO becomes insufficient. Accordingly, the glassof the present invention preferably comprises MgO in an amount of 8.5 to14 wt %, more preferably 9 to 13 wt %, most preferably 10.1 to 12 wt %.

In addition, the alkali-free glass of the present invention comprisesCaO in an amount of 1 to 3 wt % based on the total weight of oxidespresent therein. CaO is an alkali earth metal oxide, similar to MgO, andcontributes to reduce a coefficient of thermal expansion and density,inhibit the reduction of a deformation point, and enhance meltingproperty in the glass. However, when the amount of CaO is extremelyhigh, it may cause the increase of a coefficient of thermal expansionand density, and the reduction of chemical resistance, such asresistance to BHF, in the glass. When the amount of CaO is extremelysmall, the effect obtained from the inclusion of CaO becomesinsufficient. Accordingly, the glass of the present invention comprisesCaO in an amount of 1 to 3 wt %, preferably 2 to 3 wt %.

Further, the alkali-free glass of the present invention comprises SrO inan amount of 4 to 7 wt % based on the total weight of oxides presenttherein. SrO is an alkali earth metal oxide and contributes to improvethe devitrification property of the glass and the acid resistancethereof. However, when the amount of SrO is extremely high, it may causethe increase of a coefficient of thermal expansion and density, and thedeterioration of devitrification property in the glass. When the amountof SrO is extremely small, the effect obtained from the inclusion of SrObecomes insufficient. Accordingly, the glass of the present inventioncomprises SrO in an amount of 4 to 7 wt %, preferably 4 to 5.5 wt %.

Also, the alkali-free glass of the present invention comprises BaO in anamount of 0.5 to 7 wt % based on the total weight of oxides presenttherein. BaO contributes to improve the drug resistance ordevitrification property of the glass. However, when the amount of BaOis extremely high, it may increase the density of the glass and may notbe preferred in terms of environment. When the amount of BaO isextremely small, the effect obtained from the inclusion of BaO becomesinsufficient. Accordingly, the glass of the present invention comprisesBaO in an amount of 0.5 to 7 wt %, preferably 0.5 to 4 wt %, morepreferably 0.5 to 2 wt %.

In the alkali-free glass of the present invention, the sum of eachamount of MgO, CaO, SrO and BaO (the amount of MgO+CaO+SrO+BaO) ispreferably in the range of 14 to 24 wt %. Within such a concentrationrange, the effect obtained from the inclusion of alkali earth metals maybe more improved, and the devitrification property may be not bedeteriorated. More preferably, the amount of MgO+CaO+SrO+BaO is in therange of 16 to 22 wt %, most preferably 18 to 20 wt %.

In the present invention, it is preferred that the alkali-free glass hasa density less than 2.55 g/cm³. In accordance with such an embodiment ofthe present invention, the density of the glass is low, thereby easilyaccomplishing the lightening of glass products. In particular, asdevices using a glass become larger and larger, the size of the glassalso increases. In this circumstance, the reduction of a glass densitycan reduce the bending of the glass due to its weight, as well as theweight of devices using the glass. Also, when used in small portabledevices, the weight of the glass can be reduced to increase theportability of the small portable devices.

Also, it is preferred that the alkali-free glass according to anembodiment of the present invention has a coefficient of thermalexpansion (CTE) of 3.0×10⁻⁶/K to 4.0×10⁻⁶/K. In accordance with such anembodiment of the present invention, the coefficient of thermalexpansion of the glass is low, thereby providing good resistance tothermal shock. Accordingly, the glass of the present invention can beprevented from thermal contraction, deformation, bending or breakingeven if the glass is repeatedly exposed in various heat-treatmentconditions. Also, such coefficient of thermal expansion is similar tothat of the materials of TFT, thereby effectively preventing a displayfault due to a thermal expansion difference between the glass and thematerials of TFT in the preparation of a TFT-LCD using the glass of thepresent invention.

Preferably, the alkali-free glass of the present invention exhibits a T₂less than 1620° C., more preferably 1590° C., where T₂ is a temperatureat a viscosity of 10² dPas. In accordance with such an embodiment of thepresent invention, since T₂ associated with the melting (fusing) of theglass is low, the melting property of the glass can be improved, andenergy and time required for melting the glass can be reduced. Thereby,the productivity of glass products can be enhanced and production costscan be reduced.

Also, preferably, the alkali-free glass of the present inventionexhibits a T₄ less than 1260° C., more preferably 1240° C., where T₄ isa temperature at a viscosity of 10⁴ dPas. In accordance with such anembodiment of the present invention, since T₄ associated with theprocessing temperature of the glass is low, the glass can be easilyprocessed, and energy and time required for processing the glass can bereduced.

Further, the present invention provides a display device comprising theabove-mentioned alkali-free glass. That is, the display device of thepresent invention comprises, as a glass substrate, an alkali-free glasscomprising substantially no alkali metal oxide and comprising 60 to 70wt % of SiO₂; 1 to 3.5 wt % of B₂O₃; 1 to 13 wt % of Al₂O₃; 8.5 to 14 wt% of MgO; 1 to 3 wt % of CaO; 4 to 7 wt % of SrO; and 0.5 to 7 wt % ofBaO, based on the total weight of oxides present therein. Thealkali-free glass substrate used in the display device of the presentinvention has a density less than 2.55 g/cm³, a coefficient of thermalexpansion of 3.0×10⁻⁶/K to 4.0×10⁻⁶/K, a T₂ less than 1620° C., and a T₄less than 1260° C.

In particular, the display device of the present invention is preferablya liquid crystal display (LCD). The liquid crystal display such asTFT-LCD may comprise a glass substrate (panel), and the glass substratemay have the above-mentioned compositions and properties. Also, thedisplay device of the present invention may include various displaydevices such as PDP, as well as the LCD device.

Furthermore, the present invention provides a method for preparing theabove-mentioned alkali-free glass, which will be explained hereinafter.

FIG. 1 is a flow chart schematically showing the procedure of a methodfor preparing an alkali-free glass in accordance with an embodiment ofthe present invention.

Referring to FIG. 1, first, the raw material of each component containedin a glass is combined with each other to obtain the desired composition(S110). In step S110, the raw materials are combined such that 60 to 70wt % of SiO₂; 1 to 3.5 wt % of B₂O₃; 1 to 13 wt % of Al₂O₃; 8.5 to 14 wt% of MgO; 1 to 3 wt % of CaO; 4 to 7 wt % of SrO; and 0.5 to 7 wt % ofBaO are comprised, based on the total weight of oxides, in the glass,and an alkali metal oxide is not comprised therein. Preferably, in stepS110, the raw materials are combined such that 62 to 68 wt % of SiO₂, 2to 2.9 wt % of B₂O₃, 9 to 13 wt % of Al₂O₃, 9 to 13 wt % of MgO, 2 to 3wt % of CaO, 4 to 5.5 wt % of SrO and 0.5 to 4 wt % of BaO are comprisedin the glass. More preferably, in step S110, the raw materials arecombined such that 64 to 66 wt % of SiO₂; 11 to 13 wt % of Al₂O₃; 10.1to 12 wt % of MgO; and 0.5 to 2 wt % of BaO are comprised in the glass.Also, in step 110, the raw materials may be combined such that the sumamount of MgO+CaO+SrO+BaO is in the range of 14 to 24 wt %, preferably16 to 22 wt %, more preferably 18 to 20 wt %.

Next, the combined raw materials are heated to a prescribed temperature,for example, 1500 to 1600° C. to be melted (S120), and the meltedresultant is molded as a glass (S130). In step S130, the molding of theglass may be carried out by means of a float method using a float bath,but the present invention is not limited thereto. For example, in stepS130, the molding of the glass may also be carried out by means of adown draw or fusion method.

After molding in step S130, the molded glass is transferred into a lehrand slowly cooled therein (S140). Then, the cooled glass is cut into apiece having the desired size and further polished, to obtain a glassproduct.

Thus, the alkali-free glass prepared by the glass preparation accordingto an embodiment of the present invention has a density less than 2.55g/cm³, a coefficient of thermal expansion of 3.0×10⁻⁶/K to 4.0×10⁻⁶/K, aT₂ less than 1620° C., and a T₄ less than 1260° C. Preferably, thealkali-free glass prepared by the glass preparation according to anembodiment of the present invention has a T₂ less than 1590° C., and aT₄ less than 1240° C.

Hereinafter, the present invention will be explained in more detail withreference to the following Examples. However, it should be understoodthat the Examples are provided for the purpose of illustrations only andto better explain to a person having ordinary skill in the art, and isnot intended to limit the scope of the present invention, so otherequivalents and modifications could be made thereto without departingfrom the spirit and scope of the present invention.

Table 1 shows the compositions and properties the glasses prepared inthe Examples of the present invention, while Table 2 shows thecompositions and properties the glasses prepared in the ComparativeExamples.

EXAMPLES

Raw materials for each component were combined to have the compositions(wt %) as shown in Table 1, and the combined materials were put in aplatinum crucible and heated to a temperature of 1600° C. for 3 hours tobe melted. In the melting process, a platinum stirrer was used instirring for 1 hour for homogenization. The melted resultant was slowlycooled to 730° C., to obtain glasses corresponding to each Example. Theobtained glasses were confirmed for their composition by means of anX-ray fluorescence analysis.

Also, the obtained glasses were evaluated for the following properties,i.e., density, coefficient of thermal expansion, T₂ and T₄, and theresults thereof are shown in Table 1.

<Density>

The density of a glass was measured according to an Archimedes'sprinciple.

<Coefficient of Thermal Expansion (CTE)>

The average coefficient of thermal expansion of a glass was measuredusing a dilatometer.

<T₂>

The viscosity of a glass was measured using a high-temperatureviscometer, and when the viscosity becomes 10² dPas, the temperature T₂thereof was measured. If the temperature is 1600° C. or higher, thecorresponding T₂ was calculated using the Vogel-Fulcher-Tammannequation.

<T₄>

The viscosity of a glass was measured using a high-temperatureviscometer, and when the viscosity becomes 10⁴ dPas, the temperature T₄thereof was measured.

COMPARATIVE EXAMPLES

Raw materials for each component were combined to have the compositions(wt %) as shown in Table 2, and the combined materials were put in aplatinum crucible and heated to a temperature of 1600 to 1700° C. for 3hours to be melted. In the melting process, a platinum stirrer was usedin stirring for 1 hour for homogenization. The melted resultant wasslowly cooled to 730° C., to obtain glasses corresponding to eachComparative Example.

The obtained glasses were evaluated for the following properties, i.e.,density, coefficient of thermal expansion. T₂ and T₄, and the resultsthereof are shown in Table 2.

TABLE 1 Examples 1 2 3 4 5 6 7 8 9 10 SiO₂ 66.8 65.6 67.6 68.2 68.3 66.165.9 66.8 65.8 64.8 B₂O₃ 3.2 3.4 2.7 3.4 2.9 2.8 3.1 3.0 3.3 3.3 Al₂O₃11.5 12.3 11.3 9.5 10.0 12.5 12.2 11.2 11.9 12.8 MgO 8.9 8.9 9.8 9.910.8 10.2 10.1 12.1 11.0 10.6 CaO 1.3 1.2 1.8 2.2 1.4 2.7 2.3 1.9 2.73.0 SrO 5.2 5.3 5.5 6.1 4.9 4.5 4.3 4.2 4.1 4.6 BaO 3.1 3.5 1.3 0.7 1.71.2 2.1 0.8 1.2 0.9 Density 2.541 2.542 2.525 2.522 2.522 2.530 2.5362.519 2.529 2.536 [g/cm³] CTE 3.42 3.46 3.45 3.55 3.47 3.54 3.53 3.543.60 3.64 [10⁻⁶/K] T₂[° C.] 1612 1601 1596 1592 1587 1570 1572 1557 15541549 T₄ [° C.] 1257 1255 1254 1253 1248 1237 1236 1228 1226 1223

TABLE 2 Comparative Examples 1 2 3 4 5 6 7 8 9 10 11 12 SiO₂ 58.3 71.562.2 65.6 69.2 62.0 69.2 61.3 76.0 55.1 67.8 64.8 B₂O₃ 2.3 1.6 5.2 2.73.4 2.1 3.2 1.9 2.2 1.8 2.2 2.0 Al₂O₃ 11.6 11.1 4.3 16.4 12.7 7.2 12.29.2 11.2 8.7 3.6 5.6 MgO 13.5 8.9 13.5 8.9 4.6 12.3 9.2 11.1 2.3 11.715.8 12.3 CaO 2.6 1.2 2.3 1.3 2.2 6.7 1.9 1.2 1.5 10.2 2.1 2.5 SrO 5.54.5 6.2 4.2 5.5 5.8 1.6 5.1 4.7 6.2 5.3 8.6 BaO 6.2 1.2 6.3 0.9 2.4 3.92.7 10.2 2.1 6.3 3.2 4.2 Denisty 2.691 2.482 2.674 2.506 2.500 2.6652.480 2.705 2.432 2.784 2.595 2.659 [g/cm³] CTE 4.56 3.05 4.69 3.12 3.005.06 3.08 4.45 2.33 5.96 4.47 4.65 [10⁻⁶/K] T₂ [ ° C.] 1414 1665 13841633 1728 1389 1642 1482 1752 1297 1422 1440 T₄ [° C.] 1153 1316 11371281 1357 1134 1302 1199 1395 1072 1157 1169

As shown in Tables 1 and 2, the glasses of Examples 1 to 10 exhibit adensity less than 2.55 g/cm³, an average coefficient of thermalexpansion (CTE) of 3.0 to 4.0 (×10⁻⁶/K), as well as a T₂ less than 1620°C. and a T₄ less than 1260° C.

In contrast, it is confirmed that the glasses of Comparative Examples 1to 12 exhibit their density, coefficient of thermal expansion, T₂ and T₄higher than those of the Examples.

From the comparison of the Examples and the Comparative Examples, theglass of the present invention has good characteristics and can be moresuitably used as a substrate for a display. Also, the glass of thepresent invention has a low T₂ and T₄, and thus exhibits good meltingproperty and easy processibility, thereby reducing energy and timerequired for melting and processing the glass.

Thus, the present invention has been described in detail by specificembodiments and drawings. However, it should be understood that thespecific embodiments and drawings are given by way of illustration only,not intending to limit the present invention, and thus various changesand modifications may be made by those skilled in the art to theinvention which also fall within the scope of the invention as definedas the appended claims.

What is claimed is:
 1. An alkali-free glass comprising oxides, theoxides consisting of, based on the total weight of oxides presenttherein, 64 to 70 wt % of SiO₂; 1 to 3.5 wt % of B₂O₃; 1 to 13 wt % ofAl₂O₃; 10.1 to 14 wt % of MgO; 1 to 3 wt % of CaO; 4 to 7 wt % of SrO;and 0.5 to 7 wt % of BaO, wherein the alkali-free glass has atemperature less than 1590° C. at a viscosity of 10² dPas and atemperature less than 1240° C. at a viscosity of 10⁴ dPas.
 2. Thealkali-free glass according to claim 1, the oxides consisting of, basedon the total weight of oxides present therein, 64 to 68 wt % of SiO₂; 2to 2.9 wt % of B₂O₃; 9 to 13 wt % of Al₂O₃; 10.1 to 13 wt % of MgO; 2 to3 wt % of CaO; 4 to 5.5 wt % of SrO; and 0.5 to 4 wt % of BaO.
 3. Thealkali-free glass according to claim 1, wherein the amount ofMgO+CaO+SrO+BaO is in the range of 14 to 24 wt % based on the totalweight of oxides present therein.
 4. The alkali-free glass according toclaim 1, wherein the amount of MgO+CaO+SrO+BaO is in the range of 16 to22 wt % based on the total weight of oxides present therein.
 5. Thealkali-free glass according to claim 1, wherein the amount of SiO₂+Al₂O₃is in the range of 73 to 82 wt % based on the total weight of oxidespresent therein.
 6. The alkali-free glass according to claim 1, whichhas a density less than 2.55 g/cm³, and a coefficient of thermalexpansion of 3.0×10⁻⁶/K to 4.0×10⁻⁶/K.
 7. A display device comprisingthe alkali-free glass according to claim
 1. 8. The display deviceaccording to claim 7, which is a liquid crystal display.
 9. A method forpreparing an alkali-free glass, comprising combining raw materials ofglass to obtain an alkali-free glass comprising oxides, the oxidesconsisting of, based on the total weight of oxides present therein, 64to 70 wt % of SiO₂; 1 to 3.5 wt % of B₂O₃; 1 to 13 wt % of Al₂O₃; 10.1to 14 wt % of MgO; 1 to 3 wt % of CaO; 4 to 7 wt % of SrO; and 0.5 to 7wt % of BaO, wherein the prepared alkali-free glass has a temperatureless than 1590° C. at a viscosity of 10² dPas and a temperature lessthan 1240° C. at a viscosity of 10⁴ dPas.
 10. The method for preparingan alkali-free glass according to claim 9, wherein the combination ofraw materials is carried out for the oxides of the alkali-free glass toconsist of, based on the total weight of oxides present therein, 64 to68 wt % of SiO₂; 2 to 2.9 wt % of B₂O₃; 9 to 13 wt % of Al₂O₃; 10.1 to13 wt % of MgO; 2 to 3 wt % of CaO; 4 to 5.5 wt % of SrO; and 0.5 to 4wt % of BaO.
 11. The method for preparing an alkali-free glass accordingto claim 9, wherein the combination of raw materials is carried out forthe amount of MgO+CaO+SrO+BaO to be in the range of 14 to 24 wt % basedon the total weight of oxides present in the glass.
 12. The method forpreparing an alkali-free glass according to claim 9, wherein thecombination of raw materials is carried out for the amount ofMgO+CaO+SrO+BaO to be in the range of 16 to 22 wt % based on the totalweight of oxides present in the glass.
 13. The method for preparing analkali-free glass according to claim 9, wherein the combination of rawmaterials is carried out for the amount of SiO₂+Al₂O₃ to be in the rangeof 73 to 82 wt % based on the total weight of oxides present in theglass.
 14. The method for preparing an alkali-free glass according toclaim 9, wherein the prepared alkali-free glass has a density less than2.55 g/cm³, and a coefficient of thermal expansion of 3.0×10⁻⁶/K to4.0×10⁻⁶/K.